According to the prior art, multi-stage transmissions of a planetary design comprise planetary gear sets that are shifted using friction elements or shift elements such as clutches and brakes, and typically are connected to a start-up element, such as a hydrodynamic torque converter or a fluid coupling, that is subject to a slip effect and is provided optionally with a lock-up clutch. Such multi-stage transmissions are already generally described numerous times in the prior art, particularly for use as a motor vehicle transmission. The dissertation entitled “Systematic Synthesis and Evaluation of Multi-stage Planetary Transmissions” by Gerhard Gumpoltsberger in 2007 presented to the mechanical engineering faculty at the Technical University of Chemnitz discusses such multi-stage transmissions.
Such transmissions should have a sufficient number of gear steps and a transmission ratio that is well suited to the specific application by having a high overall gear ratio spread and favorable step changes. In addition, these transmissions should have a relatively simple design, in particular requiring a low number of shift elements, and minimize the need for double shifting when sequential shifting is performed, thereby ensuring that in each case only one shift element is switched when shifting is performed in defined groups of gears.
For other applications, such advantages are also desireable, where depending upon the application, certain aspects have a particularly high priority. Applications are known in which the weight and the construction size are a deciding factor. For instance, in the drive train of large-volume, high-pressure pumps, in the case of so-called “frac pumps” that are used to extract underground energy sources in a fracturing process, high value is placed on low weight and a small constructions size of an appropriate transmission between the drive motor and the pump, because such pumps should be as easy to transport as possible. At the same time, such transmissions must cover a necessary range of rotational speeds with the lowest possible step changes between the individual gears in order to be able to achieve a desired torque progression with as few gaps as possible. This allows the pump to be set to any desired volume flow within a prescribed volume flow range. In so doing, torques of over ten thousand Newton meters must be transmitted from the multi-stage transmission.